This invention relates to a measuring device, methods of controlling measuring devices and to methods of generating paths to be used in controlling a measuring device.
In order to ensure that a manufactured part conforms to its design, it is often the case that the part's dimensions can be checked in an automated manner. This can be performed in a number of ways, but often a probe is moved into contact with the surface of the part, and the position of the probe is noted as contact is made with the part. Multiple contacts between the probe and the part are made therefore building up a cloud of points that correspond to actual surface of the part.
Whilst some embodiments may have wider applicability, it is convenient to highlight the background of the invention with reference to pressed sheet parts, and in particular, but again not exclusively, pressed metal parts. The skilled person will appreciate that such pressed metal parts have a thickness which tends to be quite small; i.e., the part is often a thin shell. Thus, the edges of the shell tend to be thin.
It can be difficult to ensure that the probe contacts the edges of the shell because of the edge's small dimension. Small errors in the parts shape can mean the edge moves sufficiently so that a probe attempting to measure the position of the edge, miss the edge or at least do not contact it properly.
Accordingly, it is often the case that the probe is brought into contact with the part away from the region of the edge, in what may be thought of as a surface-touch. The position of this surface-touch can then be used to determine the position of the edge of the shell so that a probe can be brought into contact correctly with that edge.
However, the prior art does not calculate the path for the probe as efficiently as may be desired. In this context, it will be appreciated that in a production environment it is desired to measure parts as quickly as possible in order that the production line becomes efficient as possible.
FIGS. 1A and 1B are used to further discuss the prior art, where FIGS. 1A and 1B illustrate two examples of parts being measured by adaptive measurement in which the real position of the part 102 is not at the expected position of the part 102a. In the example shown in FIG. 1A, a probe 106 is used to perform a surface touch away from an edge 104 of the part 102. This surface-touch provides the displacement of the part from the expected position to the real position. The displacement that is calculated can then be used to determine more accurately where the edge 104 of the part 102 should be in order that the probe can more accurately measure the position of the edge 104.
In the second example, the probe 106 is used to measure the real position of the part 102 a plurality of times by making a plurality (in this example three) surface touches away from an edge 104 of the part 102. From this plurality of surface-touches, it is possible to calculate a plane of the part 102 which again can be used to allow the probe 106 to more accurately measure the position of the edge 104.